Electrolytic process for producing magnesium



Sept. 22, 1936. w MOSCHEL 2,055,359

ELECTROLYTIC PROCESS FOR PRODUCING MA GNESIUM Original Filed Nov. 25,I934 ii-i i? 1 J A INVENTOR Zgz'ULeZmmosckeZ ATTORNEYS Patented Sept.22, 1936- UNITED STATES 2,055,359 ELECTROLYTIC PROCESS FOR PRODUCINGMAGNESIUM Wilhelm Moschel, Bitteri'eld, Germany, assignor,

by mesne assignments, to Magnesium Development Corporation, acorporation of Delaware Application June 17, 1930, Serial No. 461,724

I In Germany June 20, 1929 6 Claims.

This invention relates to a process for the dehydration of hydratedmagnesium chloride and the subsequent electrolysis of the anhydrousmagnesium chloride formed thereby. The apparatus for carrying out theinvention has been made the subject matter of United States divisionalapplication Serial No. 754,479, filed November 23, 1934.

It has generally been recognized as essential 10 in the production ofmagnesium from magnesium chloride by electrolysis of a fused electrolytethat the magnesium chloride consumed in the process should be replacedby magnesium chloride which is dehydrated as thoroughly as possible. Onthe other hand it is well known to all those skilled in the art that thecomplete dehydration of the hydrates of magnesium chloride by treatingthem in a current of desiccated hydrochloric acid this being the onlyprocess hitherto feasible on a technical scale-offers great technicaldifficulties and is very expensive. An object of the present invention,therefore, is to employ such hydrates of magnesium chloride which arecomparatively easily produceable, particularly the hydrate MgClaZI-IzO,directly for feeding the electrolytic cell and to effect completedehydration in the electrolytic cell itself.

According to the present invention the hydrate to be treated isintroduced into a fused mixture 30 of chlorides, for example, a mixtureconsisting of Percent Potassium chloride 50 Sodium chlor 40 Magnesiumchloride 10 in such proportion that the content of the mixture in MgClais not allowed to rise above the proportion prevailing in naturalcarnallite. By maintaining this ratio it is possible to effect thedehydration of the magnesium chloride hydrates,

particularly of the di-hydrate, without any perceptible decomposition ofthat salt into magnesium oxide and hydrochloric acid.

Exam le 45 p MgCla and 1.8 percent of MgO. The relatively small increaseof the magnesium oxide contents is largely due to the small amounts ofmagnesium oxide contained in the di-hydrate salt as an impurity andintroduced along therewith. 5

I have further found that it is possible to feed a bath in whichelectrolytic decomposition of a melt containing anhydrous magnesiumchloride is carried out directly with the di-hydrate salt provided theaforesaid conditions are constantly 10 maintained, since the limits ofconcentration specified in the foregoing example are entirely sufficientfor carrying on the electrolysis. According to the present invention, aportion of the electrolyte impoverished in MgClz is passed 15 into aseparate chamber, preferably forming a subdivision of the electrolyticcell and separated from its main portion by a suitable partition. Intothis chamber the di-hydrate is introduced preferably in a preheatedcondition, at such a 20 rate that the MgCl: content in the fused productdoes not exceed 50 percent. Dehydration takes place quite smoothly inthe chamber and without any perceptible decomposition of the magnesiumchloride. The electrolyte thus replenished with regard to its MgCl:content is then led back into the main cell.

The annexed drawing shows a preferred form of apparatus to be used inconnection with the present invention. However, the invention is notlimited to this type of apparatus but may be carried out in any deviceas long as the above described conditions are fulfilled. Figure 1represents a plan view and Figures 2 to 4 different sections of thedevice, the broken lines in Figure 1 and their respective numbersindicating the planes in which the different sections are taken.

In a trough-shaped container a provided with a lining b of ceramicmaterial, an anode e consisting of two plates of graphite and the ironcathode j are inserted so as to. enter into the electrolyte consistingof 50 percent of NaCl, 35 percent of KCl and 15 percent of MgClz. Thecontainer is spanned by a partition 9 of chamotte which verticallyextends just below the level of the electrolyte and divides the cellproper into an anodic chamber 0 serving for the recovery of chlorine anda cathodic chamber 41 in which the metal is collected. There are furtherprovided chambers 71. and i separated from the main cell by partitionsIt and Z of ceramic material. In partition is (comp. Figure 3) extendingdown to the bottom of the container there is provided a narrow channel sthrough which, owing to the buoyancy of the chlorine ascending in theanode chamber, some of the electrolyte is caused to enter into thechamber h. Into this chamber also the di-hydrate at the rate required bythe invention is introduced and immediately gives off its water contentby evaporation, whereupon the electrolyte replenished with regard to itsmagnesium chloride contententers chamber 2 through a gap provided belowpartition 9, and then flows back into the main chamber d, through theopening provided below the partition I. The continuous circulation ofthe electrolyte in the manner' described is sufflcient for maintainingthe necessary temperature in chambers h and 2'. However, it is alsopossible to individually heat these chambers in any known manner, forinstance, by means of an alternating current.

The present invention is not limited to the dehydration of thedi-hydrate MgCl2.2HzO, as other hydrates, such as the tetra-hydrateMgC12.4HzO, may also be treated in a similar manner. However, thedehydration of other hydrates to a point corresponding 1170 thedihydrate when carried out in the usual manner,

for example, in a reverberatory furnace, offers no difiiculties. Itherefore preferably employ the di-hydrate as the starting material inmy process.

Another form of carrying out the present invention consist in supplyingthe magnesium chloride to the electrolyte by introducing the hydrates inan entirely separate container into the fused electrolyte which for thispurpose must be led out of the cell proper. This mode may beadvantageous when a large number of cells must be continually suppliedwith fresh electrolyte, as it is possible, in this case, to perform theregeneration of the electrolyte of a plurality of cells within a singleapparatus.

I claim:

1. The process of electrolytically producing magnesium and chlorine frommagnesium chloride which comprises passing a current through a fusedbath containing magnesium chloride and alkali metal chlorides andcontinuously introducing preheated di-hydrated magnesium chloride into acompartment of said bath in communication with the fused chlorides butout of contact with evolved chlorine, said preheated dihydratedmagnesium chloride being introduced in such amounts that the content ofthe bath in magnesium chloride does not rise above 50 percent, wherebythe added chloride is first dehydrated and then decomposed by thecurrent into its constituents.

2. The process as defined in claim 1 wherein the bath is maintained at atemperature of about 700 C.

3. The process of electrolytically producing magnesium and chlorine frommagnesium chloride which comprises passing a current through a fusedbath formed by adding to a mixture composed of 50 percent of potassiumchloride 40 percent of sodium chloride and 10 percent of magnesiumchloride, hydrated magnesium chloride to bring the content of the bathin magnesium chloride to about 25 percent and continuously introducingpreheated di-hydrated magnesium chloride into a compartment of said bathin communication with the fused chlorides but out of contact withevolved chlorine, to maintain the content of magnesium chloride in thebath substantially constant.

. 4. The process of continuously electrolytically producing magnesiumand chlorine from magnesium chloride in a cell having a plurality ofinter-connected compartments, which comprises passing a current througha fused bath containing magnesium chloride and alkali metal chlorides inone compartment of said cell to decompose said magnesium chloride intomagnesium and chlorine, causing the evolved chlorine to aid in effectinga transfer of a portion of the bath depleted in magnesium chloride fromsaid compartment into another compartment, adding preheated di-hydratedmagnesium chloride to the portion of the bath transferred to said othercompartment while maintaining said portion in a fused condition, saidpreheated di-hydrated magnesium chloride being added in such an amountthat the content of magnesium'chloride in the final mixture is less than50 percent, returning the fused mixture to said first compartment andthere electrolyzing the same.

5. A continuous electrolytic process for producing magnesium andchlorine from anhydrous magnesium chloride in a cell having a pluralityof interconnected compartments, said process comprising passing acurrent through a fused bath containing anhydrous magnesium chloride andalkali metal chlorides in one compartment thereof to decompose saidmagnesium chloride into magnesium and chlorine, maintaining said bath atabout 700 C., causing the evolved chlorine to aid in effecting atransfer of a portion of the bath depleted in magnesium chloride fromsaid first-mentioned compartment into another compartment, addingpreheated di-hydrated magnesium chloride to the portion of the bathtransferred to the second-mentioned compartment, said preheateddi-hydrated magnesium chloride being added in such an amount that themagnesium chloride content of the final mixture is less than 50 percent,and returning the fused mixture to the first-mentioned compartment andthere electrolyzing the same.

6. The process of electrolytically producing magnesium and chlorine frommagnesium chloride which comprises passing an electric current through acell containing a fused bath of magnesium chloride and alkali metalchlorides, continuously introducing di-hydrated magnesium chloride intoa compartment within said cell in communication with the fused bath butout of contact with evolved chlorine, and maintaining said di-hydratedmagnesium chloride in the compartment to dehydrate the same through themedium of the bath temperature, said di-hydrated magnesium chloridebeing introduced in such amounts that the content of the cell bath inmagnesium chloride does not exceed 50 percent.

WILHELM MOSCHEL.

